As conventional techniques in the above-described field, those disclosed in Japanese Unexamined Patent Publication No. H7-288106 and Japanese Unexamined Patent Publication No. H10-64479 are known. In either gas discharge tube, a barrier wall made of metal is disposed on an electric discharge path between an anode part and a cathode part, and a small hole is formed on the barrier wall so as to narrow the electric discharge path. In such a structure, light with high brightness can be obtained by the small hole on the electric discharge path. In particular, in the gas discharge tube of Japanese Unexamined Patent Publication No. H7-288106, brightness is further increased by extending the length of the small hole, that is, a portion of the electric discharge path that is narrowed. On the other hand, in the gas discharge tube of Japanese Unexamined Patent Publication No. H10-64479, higher brightness is achieved by disposing a plurality of barrier walls in addition to extending the length of the small hole.
The demand for higher brightness in the technical field of gas discharge tubes has been comparatively satisfied by the techniques disclosed in the above-described patent publications.
However, when the narrowed portion of the electric discharge path is extended in length, an electric discharge is less liable to occur. To avoid this problem, in the gas discharge tube disclosed in the above second patent publication, a plurality of metal barrier walls are disposed to generate an electric discharge step by step; however, there is a problem in that this complicates a power supply circuit.
Therefore, an object of the present invention is to provide a gas discharge tube which can securely generate an electric discharge, regardless of the length of a portion of the electric discharge path that is narrowed.